To test whether Eq. (REF ) is an appropriate definition, a basic criterion is that curvatures should be negative [1]}, [2]}, [3]}. However, from Eq. (REF ), we find the typical sectional curvatures are positive. In fact, it can be further proved that the typical sectional curvatures are always positive, if the metric has the form
\(d\mathcal {C}^2=(dUU^{\dagger }|f(n)|dUU^{\dagger }).\) 
